1. Field of the Invention
The invention relates to independent support of an outlet manifold in a steam reformer furnace, and more specifically related to independent support of an outlet manifold within a heated enclosure of a steam reformer furnace.
2. Description of the Related Art
A steam reforming process is a well-established catalytic process that converts natural gas or light hydrocarbons into a mixture containing a major portion of hydrogen. The steam reforming process has gained more and more importance with the increasing demand of various types of gases for the chemical and petrochemical industries, including hydrogen, ammonia, and others. In particular, hydrogen has become a very important product for the refinery desulphurisation and hydrocracking process units.
FIG. 1 is a perspective schematic view of a known exemplary reformer. FIG. 2 is an end schematic view of the reformer shown in FIG. 1. FIG. 3 is a detail end view of a manifold guide system used in the exemplary reformer shown in FIG. 1. The figures will be described in conjunction with each other. A steam-hydrocarbon reformer 2 generally includes three principal sections on the process side of the furnace internals, namely an inlet system 4, a plurality of catalyst tubes 6, and the outlet system 10 with the catalyst tubes being contained in a furnace firebox 8. The inlet system 4 is generally located on an upper portion of the reformer 2 and contains a heated steam-hydrocarbon mixture that enters through an inlet 5. The inlet system 4 directs flows of the mixture to the catalyst tubes 6. The catalyst tubes 6 are internally filled with a catalyst that assist in breaking the molecular bonds of the mixture to allow formation of the desired gases. A variety of catalysts (nickel-based) are available for a given feed and product requirement. The reformer reaction process is endothermic, requiring high level heat input. Because the process requires high heat input levels, the catalyst-filled tubes are placed vertically in the radiant firebox section of the furnace. The steam-hydrocarbon mixture is typically preheated outside the radiant section to minimize the radiant heat load and, therefore, the furnace fuels requirement. The catalyst tubes 6 are arranged typically in multiple rows of “once-through” parallel “passes”, with the preheated inlet mixture entering the top of each catalyst tube, and exiting at the bottom. Two rows 7A, 7B with five catalyst tubes each are shown only for illustrative purposes with the understanding that the actual numbers of manifolds and tubes likely will be different than shown. For example, one known reformer uses four rows and 54 tubes per row. Once the reformed gas exits the catalyst tubes 6, it is collected in the outlet system 10. The outlet system 10 typically includes a manifold 12A, 12 B (generally “12” and likewise for other numbers) for each row of catalyst tubes 6. The outlet manifolds 12 are pipes running horizontally below each row 7 of catalyst tubes 6. In the illustrated embodiment, a manifold 12A would receive flow from the tube row 7A, and a manifold 12B would receive flow from the tube row 7B. The manifolds 12 in turn are connected to a central transfer line 14A through connection tees 16 for aggregating multiple manifolds. Further, more than one set of manifolds and transfer lines can be used, such as another transfer line 14B from another set of manifolds (not shown), which may be from another section in the same reformer or another reformer. The reformed gas from the transfer line 14A (and 14B) can flow into an external process gas waste heater 18 for cooling of the gas. The heater 18 can therefore heat other flow streams using the heated reformed gas output through an infeed line 20 that exits through an outfeed line 22, such as to generate steam or similar duties. The effluent in the effluent line 19 from the heater 18 is typically cooled to permit further reaction in further downstream equipment. Safe and reliable operation of the reformer furnace depends on the disposition of the catalyst tubes, manifolds, transfer lines, the external process gas waste heater, and connections therebetween.
One of the critical components on the reformer is the supports for the outlet system 10. The manifolds 12 are enclosed within an insulated header box 26 and are supported within the header box. A plurality of manifold upper guides 36 and a plurality of manifold lower guides 38 are attached on each side of the header box with a vertical gap therebetween and a manifold support slide lug 40 is attached to the manifold 12 that is slidably disposed between the manifold upper and lower guides with some lateral and vertical clearance. Thus, the manifold support slide lug 40 on the manifold can support the manifold between the manifold upper guide 36 and the manifold lower guide 38 on each side of the header box 26 and still allow some lateral, vertical, and longitudinal movement of the manifold.
The header box 26 for each manifold is connected to the firebox floor 9 of the firebox 8. The header boxes 26 are supported by header box supports 28 that in turn are supported by a datum 30, such as the ground. The transfer line 14 is supported by a transfer line support 32 that in turn is supported by the datum 30. The transfer line support 32 includes a saddle 34 that may closely fit the contour of the transfer line.
Heating from ambient conditions causes thermal expansion and growth of the components and in general deformation or bowing and other thermal movement. Some flexibility is designed into the systems. There is a need for the components to be physically supported and guided suitably, yet allow for their growth in size due to thermal expansion. While the inlet system, the catalyst tubes, and the outlet system are each supported, any one support method could have an influence on the others. The piping of the inlet system 4 is supported on fixed supports as well as springs supports. The catalyst tubes 6 are supported by constant spring hangers. The catalyst tubes 6 are connected to the manifolds 12 of the outlet system 10 via stub pipes. The manifold tubes are supported by the upper and lower guides 36, 38 in combination with the slides 40, the header boxes are supported by the header box supports 28, and the transfer line 14 is supported by the transfer line support 32, as described above.
However, the thermal expansion can be so great that the above described support system is incapable of sufficient support that still allows the required growth from the thermal expansion during operations. The expansion can cause twisting and rupture or breakage in one or more of the components and their connections to is adjacent components.
FIG. 4 is a side schematic view of the reformer shown in FIG. 1. FIG. 5 is a top schematic view of the outlet system shown in FIG. 1. The figures will be described in conjunction with each other. During operation, the temperatures can be, for example, about 1600° F. (870° C.) for the manifold and about 250° F. (120° C.) for the header box. The amount of thermal expansion can cause the firebox floor 9 to bow vertically to a floor position 9′ in the middle of length of the firebox 8 or at other locations. The header box 26, being attached to the firebox floor 9, is forced to bend vertically to a header box position 26′. The manifold 12, being supported and guided by the guides 36, 38 of the header box, also bends vertically to a manifold position 12′. Thus, the outlet system 10 can expand in a longitudinal direction 46 and is bent into a different position in a vertical direction 42 during operation.
Concurrently, the transfer line 14 bends laterally due to thermal expansion to a transfer line position 14′. The connection tees 16A, 16B, being attached to the transfer line, bend laterally to connection tee positions 16A′, 16B′. The manifolds 12A, 12B, being attached to the connection tees, bend laterally to manifold positions 12A′, 12B′. Thus, the outlet system 10 is bent into a different position in a lateral direction 44 during operation.
The consequence is failure at multiple locations. Stresses induced on the various components exceed the allowable stresses and the connections, manifolds, and joints fail.
Therefore, there remains a need to provide an improved support and header box system for the outlet system components.